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made measurements of chemical reactions in sealed containers and observed that the mass of reactants before a reaction was equal to the mass of the products after the reaction
law of conservation of matter
states that when a chemical reaction occurs matter is neither created nor destroyed but only changed
studied compounds and observed that the elements that composed them were always in a certain proportion by mass (the law of definite proportions)
an explanation based on many observations and supported by the results of many investigations
a fact of nature that is observed so often that it becomes accepted as truth (does not explain why something happens)
discovered that atoms were not tiny solid balls that could not be broken up into parts but are composed of electrically charged particles
proposed a model of an atom in which electrons orbited a central, positively charged nucleus
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